146 MR. darwin's work and 



and its modifications may, occasionally, all find the 

 conditions fitted for their existence ; and though they 

 come into competition, to a certain extent, with one 

 another, the derivative species may not necessarily 

 extirpate the primitive one, or vice versa. 



Now palaeontology shows us many facts which are 

 perfectly harmonious with these observed effects of the 

 process by which Mr. Darwin supposes species to have 

 originated, but which appear to me to be totally 

 inconsistent with any other hypothesis which has been 

 proposed. There are some groups of animals and 

 plants, in the fossil world, which have been said to 

 belong to " persistent types/' because they have per- 

 sisted, with very little change indeed, through a very 

 great range of time, while everything about them has 

 changed largely. There are families of fishes whose 

 type of construction has persisted all the way from tl>e 

 carboniferous rock right up to the cretaceous; and 

 others which have lasted through almost the whole 

 range of the secondary rocks, and from the lias 

 to the older tertiaries. It is something stupendous this 

 — to consider a genus lasting without essential modi- 

 fications through all this enormous lapse of time while 

 almost everything else was changed and modified. 



Thus I have no doubt that Mr. Darwin's hypothesis 

 will be found competent to explain the majority of 

 the phenomena exhibited by species in nature ; but in 

 an earlier lecture I spoke cautiously with respect to its 

 power of explaining all the physiological peculiarities 

 of species. 



There is, in fact, one set of these peculiarities which the 

 theory of selective modification, as it stands at present. 



